PIANO-PLAYER, THE

471

the secondary diaphragm 13 ; the part 146 13 kept partially exhausted of air, and thus, when air is admitted to the other side of the diaphragm, the difference of pressure causes it to move, carrying with it the secondary valve 15, 16 to which the diaphragm is joined. This movement closes the opening from the open air to the channel 17, and puts this channel

PIG. 1.

into connection with the exhausted chamber 146, so that air is withdrawn from the pneumatic 18, causing it to collapse, and to lift the action 20 by means of the connecting rod 19. There is a tiny hole 8a called a bleed-hole connecting the chamber 9 with the tube 6 ; so that when the perforation has passed across the aperture in the tracker-bar and the slot is once more closed the pressure becomes equalised on both sides of the diaphragm 8. This then falls and allows the primary valve to fall also. The air is therefore sucked out of the tube 12, the valve 13 is drawn back, and the pneumatic 18 is allowed to open, ready to give another blow. All this is very similar to the operation of the pneumatic action in the larger pipe-organs.

§ (3) BELLOWS AND RESERVOIR.—The two chambers 9 and 14 of Fig. 1 are kept ex-

FIG. 2.

hausted by being' connected through the action-box 8 (Fig. 2), trunk 7, and the bellows-board 5 to the reservoir 6.

The reservoir is a bellows kept open by a spring ; the air has to be continuously removed from it by working the foot-pedals 1, which through the pedal-bars 2 force open the bellows 3 against the pressure of the spring 4. The pneumatics of a pipe-organ are worked by air, which is at a pressure of about 30 cm. of water above that of the atmosphere; but while it is obvious that both primary and secondary pneumatics might be arranged to work with an air pressure which is either above or below the atmospheric pressure, the latter is now always used in players, as the reduced pressure holds the music roll down against the tracker-bar, and leakage is avoided.

§ (4) MOTOR.—To carry the music roll from the roll 3 on to the take-up spool 1 of Fig. 1, the latter is rotated by a pneumatic motor, which is also driven by air passing to the reservoir 6. The motor consists of five simple bellows

FIG. 3.

1, 2, etc. (Figs. 3 and 4), each joined by a connecting rod 4 to a five-throw crank-shaft 5, the cranks being at 72° to one another. The same shaft works slide-valves 7 by arms 6, which alternately admit air to each of the bellows and put it into communication with the reservoir through the exhaust 8.

§ (5) EXPRESSION.—The player as it has so far been described would run at a constant speed, strike every note with the same force, and altogether fail to pick out a melody. Thus although its execution might be perfect, it would give none of the light and shade and no variety of tempo (except such as might be incorporated

FIG. 4.